Wednesday Word(s) of the Week: Island Biogeography

bi•o•ge•og•ra•phy noun [bahy-oh-jee-og-ruh-fee]: the study of the geographical distribution of living things1.

A giant Galapagos tortoise observes the land below near the rim of the Alcedo Volcano.

Photograph by Sam Abell, National Geographic Stock.

In its broadest sense, island biogeography is the study dedicated to figuring out why certain plants and animals came to exist on a specific island or group of islands. What factors allowed a species like the Galapagos turtle to end up in a small cluster of islets over a thousand miles away from any continent? How did the plump little Kiwi find its way to New Zealand without any wings to fly over the sea? Why can the same species of butterfly be found on two distinct islands separated by an entire ocean? These are the questions that biogeography aims to answer by observing populations and taking into account biotic (living) and abiotic (nonliving) environmental factors.

The obvious isolation of islands away from mainland sources of plants and animals has allowed geographers and biologists to think outside of the box and expand their understanding of the factors influencing evolution and species migration. The fact that many seemingly deserted islands in the middle of the ocean can be teeming with life is testament to the journeys that some animals will travel will travel–often covering vast amounts of water– and the adaptability of species to new environments.

A petrified tree floats in the crystal-clear waters of the Palmyra Atoll in Polynesia’s Line Islands.

Photograph by Randy Olson, National Geographic.

And by vast amounts of water, I really do mean incredible distances from continents. One such example is the Pitcairn Islands, located about halfway between Peru and New Zealand in the middle of the South Pacific Ocean–about as isolated as “neighboring” Easter Island 1,300 miles away. And yet, an abundance of plant and animal life existed on and around the four small islands well before the mutinous crew from the Bounty arrived there two centuries ago, and possibly before ancient Polynesians paddled ashore thousands of years ago. Many unique plant species are found on Henderson Island, an uninhabited raised coral atoll north of the main island of Pitcairn. Nearby Oeno island has a number of sea snail species that are only found on its reefs. The only familiar plants on the islands seem to be coconuts and imported Araucaria trees. Pitcairn, a mere five square kilometers wide, is the only inhabited island, which has unfortunately been extensively transformed through wood harvesting and agricultural plantings.

Can
you think of any unique species that are only found on islands? For a place to
start, look at the island of Madagascar…

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